Image information digitalization has brought the major break to the field graphic art, and CTP (Computer to Plate) which outputs image information to be imparted to a printing plate as digital information directly to a printing plate from a computer to produce a plate is extremely effective in increasing the quality of printing and in decreasing cost and, is significantly paid to attention. For example, a positive resist layer on a base plate is exposed according to the information (image information) of a pattern input to an exposing apparatus as digital information from a computer, and a given development treatment is effected to form a pattern composed directly of a resist, thus, the whole plate or a part thereof can be formed. The application range of CTP is wide, and applications to direct production of various plates such as flat plates, concave plates, convex plates, gravure plates and the like are being examined.
On the other hand, as lights for exposure of various resist materials, there are utilized ultraviolet ray, far ultraviolet ray, electron beam, X ray, laser light, gamma ray and the like. The lights have respective characteristics, and use of semiconductor lasers of which apparatus can be miniaturized easily has been investigated. Among others, a near infrared semiconductor laser (λ=830 nm) has merits that output is high and additionally, its apparatus can be miniaturized, and a bright room exposure operation under natural light or interior illumination is possible, thus, is useful as a light for exposure of a resist in the case of CTP as described above and the like.
Positive photosensitive compositions responding to laser lights in the near infrared wavelength region are described in Japanese Patent Application Laid-Open (JP-A) Nos. 10-90881, 10-161304, 11-231515 and 2001-166460.